hey everyone I have a flowering room that is 6'x6' and 5.5' tall I have a 8" exhaust with about 25' of ducting running to the chimney and a 6" intake on about 25' ducting running from the basement into my grow room. I had to get a fan speed controller for the 8" fan because the room was creating a vacuum pulling the floor up and mylar off the walls. I have 3 600 hps in the room. I turned them all on and set the thermostat at 75* to test the system. My problem is the fan kicked on after a couple mins. and doesn't kick off at all. Does this seem like it is enough movement the room is just under 200 cubic foot and the 6" fan is 450 cfm so not counting the ducting (not sure how to calculate it in) the room should be able to have a full air replacement every 30 seconds or so.... The intake fan is blowing in and exhaust is sucking it out. In that I mean both vortex fans are located out side of the grow room. All I can think of if this is not enough is to hook the exhaust fan up to the hoods and sucking the air directly past the lights rather than just from the room but the lights are on movers so not sure if this will put to much stress on the movers do to the extra drag from the ducting...... and I currently don't have the glass in the reflectors to get the extra lumens possible. I think the room is sticking around high 80s with all the lights on. Thanks for reading and am open for any input.
personally i think 25 ft of ducting will cause alot of resistance, but if you do decide to keep this amount of ducting then just your exaust should be more than just 2 inches bigger than your intake, and 465 cfm for a 8" fan is really not alot, imo its the +/- pressure thats the problem, i would use both fans as exausts with 2 separate holes in the top of your grow room, and just have one big passive intake, this would solve some of your problem, another solution would be to have one fan exausting and the other fan cooling your lights,along with a pasive intake, this as well would solve your problem. the key to good ventilation is to ave an intake about 1/3 the size of your exaust, this means 1/3 the size of holes and 1/3 the size of cfm